Actually, it's a grace. We are not to worry about tomorrow. I simply don't have the cognitive strength to think about things I can't do anything about for long. And lately, I haven't been able to do much about anything! I think it has given me some further experience in these two verses:
You will keep him in perfect peace,
Whose mind is stayed on You,
Because he trusts in You.
And Matthew 6: 34
Therefore do not worry about tomorrow, for tomorrow will worry about its own things. Sufficient for the day is its own trouble
I can say experiential that there is peace when you can rest in Him. This enforced rest and peace is necessary for joy. Trusting Him is necessary for joy